1. Field of the Invention
The present invention relates to a communications network, and more particularly, to a protocol for a media access controller for a mobile ad-hoc network.
2. Description of the Related Art
A major challenge in a mobile ad-hoc network (MANET) is to design a media access controller (MAC) that can handle requirements for multiple media accesses to the MANET in real time. The challenge stems from the fact that the MANET does not have a stationary and centralized coordinator such as a base station and that its topology changes frequently. Further, the MAC should satisfy the needs for quality of service (QoS) in real time and for portability or mobility by being able to accommodate smaller and lighter batteries.
Conventional MACs for a wireless local area network (WLAN) usually use a carrier sense multiple access (CSMA), which is an asynchronous random access mechanism, due to its simple configuration and ease of implementation. However, due to the problem of a “hidden terminal,” a multiple access with collision avoidance (MACA) protocol using a request-to-send (RTS) frame and a clear-to-send (CTS) frame was suggested.
IEEE802.11 working group developed a MAC protocol as an international standard for the MANET as well as the WLAN. The MAC protocol uses a carrier sense multiple access/collision avoidance (CSMA/CA) mechanism as a distributed coordinate function (DCF). To avoid collisions, each equipment on the WLAN monitors when the other equipment attempts to and when waits to transmit a packet. However, such a random access is not suitable for real time and periodic traffic. To complement this, polling-based real time traffic is supported by a centralized point coordinator function (PCF), which, however, is not suitable for the MANET environment that does not have a centralized coordinator. Therefore, a variety of protocols have been suggested to secure the quality of real-time traffic.
A multiple access with collision avoidance/piggyback reservation (MACA/PR) protocol is a time division multiplex (TDM) combined MAC protocol in a broad sense and uses a non-persistent CSMA mechanism for a Datagram. In this protocol, a node does not respond using the RTS and the CTS frames in its reservation table by sensing the state of a channel after a free window period. Instead, the node responds using the propagation and maintenance of reservation tables managed by neighboring nodes. Therefore, the operation of the reservation table is complicated. In addition, when a new node is added to a system, the new node should learn present reservations in a listening mode for a sufficient period of time and wait until it receives a reservation table from its neighboring nodes. Unlike a slot mechanism, an un-slot mechanism is freed from the difficulty of synchronization. However, as the provision and synchronization of a clock signal are not a problem for advanced communication systems such as a global positional system (GPS), a slotted MAC has begun to draw attention and, accordingly, diverse protocols have been suggested.
An enhanced time division multiple access (E-TDMA) protocol is reserved at a talk-spurt level. The reservation process is a five-phase procedure and takes a long time. A time division multiple access/frequency division duplex (TDMA/FDD) protocol is reserved on a call basis and not frequently used due to silence.
As described above, although a variety of slotted protocols have been suggested, these protocols additionally require the GPS or a station functioning as a centralized controller. Further, system synchronization is difficult and the operation of the protocols is complicated.